The above is one of my hives with a large clump of bees suspended beneath it. Its been like this for four weeks now. The hives, as you can just about see, is on a mesh floor only. There is now, on last inspection, no sign of any brood but the bees are not agitated as one might expect. This lends weight to what a few people have suggested; that the bees have swarmed, but the Queen (being clipped) was not able to get away. Therefore the swarm tried to return but got confused and became stuck beneath the hive.
The only problem with this is that no new Queen seems in evidence. Either way on last inspection I swpt the bees from beneath the hive into a tray and tipped them into the brood box. Next week, June 5th, we'll see whats happened.
Subsequent to this, I scrapped the bees into a Nuc lid and dumped them into the hive brood box. Problem solved; the following week no bees beneath and fresh eggs in the frames.